Changes to fix Issues #81 and #96

For Issue #81
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Added a div surrounding the "+" link with a class of <code>board-add-icon</code> in **board_show.php** and styled with two new styles in **app.css**.

For Issue #96
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Updated custom jQueryUI to include Datepicker. Added CSS and images (within CSS) for Datepicker. Updated **task_new.php** and **task_edit.php** to use the Datepicker.